1. Field of the Invention
This invention relates in general to battery charging systems and more particularly, to battery charging systems that identify battery information.
2. Description of the Related Art
Many rechargeable batteries, such as those commonly found in cellular telephones, include a memory device in addition to the battery cells, such as an erasable programmable read-only memory (EPROM) or an electrically erasable programmable read-only memory (EEPROM). The memory device stores important information about the battery in which it is embedded. For example, the memory device can include information about the battery such as the battery type used (example: whether the battery is a nickel-cadmium battery or a lithium battery), and specifics concerning the charging regime to be employed. Moreover, the memory device can store “fuel gauge” information, which can enable the host device (the device to which the battery supplies power) or charger to determine accurately the state of charge of the battery such as a measurement based on measured battery voltage.
In addition to a memory device, many rechargeable batteries contain a thermistor. Incorporating a thermistor into a rechargeable battery permits a microprocessor in the battery charger to monitor the temperature of the battery during the charging process.
The life of these “smart” batteries is therefore extended by insuring that the battery cells are not overcharged, which could permanently damage them. However, batteries that contain a memory device and a thermistor typically include separate contacts for each of these components. The use of “smart” batteries although useful is not without its shortcomings. One shortcoming is the typical “smart” battery configuration increases the number of contacts that the battery, the host device and the charger requires for proper operation. An increased number of contacts in turn adds to the expense and the physical dimensions of the battery as well as the host device and the battery charger.
Accordingly, a need exists for a “smart” battery circuit with a non-volatile memory device and thermistor which reduces the number of contacts required.